Process for heating and humidifying blast for metallurgical furnaces



Feb. 7, 1961 o. R. RICE 2,970,901

PROCESS FOR HEATING AND HUMIDIFYING BLAST FOR METALLURGICAL FURNACES 3 Sheets-Sheet 1 Filed Oct. 28, 1959 NUNDOW m mv uuaaom 3&8 2w WW mobs 1 3: a

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o. R. RICE Feb. 7, 1961 2,970,901

PROCESS FOR HEATING AND I-IUMIDIFYING BLAST FOR METALLURGICAL FURNACES 3 Sheets-Sheet 2 Filed Oct. 28, 1959 mumaow m u m moaiual 55m Feb. 7, 1961 Filed 001;. 28, 1959 O. R. RICE PROCESS FOR HEATING AND HUMIDIFYING BLAST FOR METALLURGICAL FURNACES 3 Sheets-Sheet 3 SPECIAL COKE 0"" MS HSITWE DISPLACEMENT COMPRESSOR DIE LEGEND PRESSURE SWITCH TEMP. CONTROL VALVE.

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a T TOPMS Y United States Patent PROCESS FOR HEATING AND HUMIDIFYING BLAST FOR METALLURGICAL FURNACES Owen R. Rice, Pittsburgh, Pa., assignor to Koppers Company, Inc., a corporation of Delaware Filed Oct. 28, 1959, Ser. No. 849,209

' 8 Claims. 01. 75-41 This invention relates in general to improvements in the blast for metallurgical furnaces, and more particularly, for iron blast furnaces.

The primary aim of the invention is to augment the heating and humidifying of the blast in a manner that greatly reduces the cost of preparing a blast of a desired higher heat and moisture content.

In contrast to the dry-blast 'era of years ago, it has been found desirable to add moisture in the form of steam to the cold blast furnace blast and to supplement the heating of the blast from stoves or recuperators by adding additional heat to the hot blast before it enters the blast furnace.

The addition of steam to the cold blast in amounts up to 25 grains of steam per cubic foot of blast has been found beneficial before the hot blast enters the furnace hearth from the tuyeres; the hydrogen of the steam being a valuable reducing agent in the blast furnace. The steam or water vapor is usually added to the cold blast air from the blowing engine, before the blast is heated in stoves or recuperators, in order to secure a constant blast temperature and humidity, and the steam so introduced is costly, since the addition of 10 grains of steam per cubic foot of blast at a medium size blast furnace, involving 7200 pounds of steam per hour, costs about $5.00 an hour, representing over 200 boiler house power.

Accordingly, the present invention provides a process of preparing the blast which reduces the cost of steam for humidifying the blast by forming about one-half of theamount of water vapor for humidifying the hot blast during the supplemental heating of the same to higher temperature of 300 F. or more to augment the heat of .the blast. This is done by burning high hydrogen containing gas in amounts to supply half the humidity directly in the hot blast, thereby forming about one-half the amount of water vapor in the blast as a product of the combustion. High degree of humidity is attained with a reduction in cost for the steam since the additional water vapor is formed as the product of combustion that produces the higher temperature in the blast.

The addition of both heat and moisture to the blast in the aforesaid manner can be attained with preheating by recuperative preheating, as well as with regenerative preheating, by burning the high hydrogen-containing gas directly in the hot blast after the recuperators or stoves. Recuperators are not now used to the extent that they once were. Recuperators can be used in accordance with this invention, however, in the form of supplementary blast heating. In some cases, recuperators may be cheaper than the regenerative system of stoves, but generally, recuperators cannot attain temperatures as high as stoves because of the limitation of construction material. Consequently, the direct heating of the blastfurnace air is a valuable adjunct to a recuperator since itmakes possible the attainment of high blast tempera tures by preheating in a recuperator more inexpensively than by preheating with a system of regenerative stoves; This may result in a return to the use of recuperatorst However, this is only an incidental feature of the invention. The invention is particularly desirable and advantageous for use with stoves in regenerative heating.

As an example of the invention, a substantial saving in cost of steam, with recuperative heating, may be attained, since this mode of augmenting the heat of the hot blast for blast furnaces lends itself to supplying the blast to the furnace, for instance, at a heat of 1400 F. with 11 grains of water per cubic foot of dry air, by preheating the air recuperatively to 1100" F. with addition of steam but limited to 5 grains moisture per cubic foot, and then burning high hydrogen gas directly in this moist hot blast in amount to raise its temperature to 1400 F. The combustion of the amount of fuel in such a case for this rise in temperature, results in the formation of 6 grains H O, which is automatically taken up by the hot blast passing to the hearth of the blast furnace, and gives the blast the necessary 11 grains of moisture per cubic foot, without extra cost for steam, to produce the additional one-half of the total humidity in the blast for the furnace bed.

In accordance with this invention, a substantial saving in cost of steam, with augmenting the heat of the hot blast from stoves, may thus be attained also, since this mode of augmenting the heat of the hot blast for blast furnaces lend itself to supply ofthe blast to the furnace at a heat of 2000 F. with 25 grains of water per cubic foot of dry air, by preheating the air regeneratively in stoves to 1500 with 14 grains of water per cubic foot and added in the form of steam to the cold blast before the stoves, and then burning high hydrogen-containing gas directly in the hot blast from the stoves in amount to raise its temperature to 2000 F. This combustion results in the formation of 11 grains of H 0, which is auto matically taken up by the hot blast passing to the hearth of the blast furnace and gives the blast the necessary 25 grains of moisture per cubic foot, without extra cost of steam to produce approximately the additional one-half or more of the total humidity desired in the blast.

If more humidity is desired in the blast. furnace air, it is secured by reducing the amount of heating effected 'recuperatively, or regeneratively, thus throwing more heating load on the heat augmenting step," thereby calling for firing more high hydrogen-containing gas, such as, for example, coke oven gas, which introduces more (H O) water vapor in the blast as a product of combustion.

The combustion of gas, as directly in the hot blast aforesaid, results in a deficiency of oxygen in the blast 'The hydrogen of the H 0 combustion products is a valuable reducing-agent in the blast furnace, and the CO is a coke consuming agent forming the useful reagent CO.

The direct heating of the preheated blast air for blast furnaces by burning hydrogen-containing gas with part of the total air for the blast furnace from the blower, can be utilized in existing plants, as well as new plants, without the necessity for controlling the amount of the total air and hydrogen-containing gas, that is burned to aug- '3 ment the preheated hot blast by,--and in accordancewith, changes in the control of the total air for the blower in a central control station; the high hydrogen-containing gas may be any'conventional fuel of'high hydrogen content,'for example, natural gas. The amount of total-air and high hydrogen-containing fuel that is utilized in the direct heating of the preheated blast for blast furnaces, tosimultaneously augment the water vapor or moisture content for beneficiating the blast and to provide additional hydrogen as a source of reductant, can also be advantageously carried out with automatic control of the amount of fuel and total air consumed in the direct heating of the hot blast by, and in accordance with, "changes in the control of the total air for the blower in a central control station, as described and claimed in my copending application Serial No. 765,192, filed October 3, 1958, entitled Direct Heating of Blast Furnace Air 'Blast, of which this application is a continuation-in-part. Other objects and advantages of the invention appear from the following description and claims.

The accompanying drawings show, for the purpose of exemplification, certain practical embodiments of the invention without limiting the claims thereto.

Fig.1 is a diagrammatic view of apparatus for carry- "ing out the method of adding both heat and moisture to the cold blast by means of recuperative preheating for the initial heating of the blast, followed by the step of burning a high hydrogen-containing gas directly in the hot blast from a recuperator after the blower for the total air blast for the blast furnace, without control by the blower control of the amount of air and fuel burned in direct heating. Fig. 2 is a diagrammatical view of apparatus for carrying out the same method by means of regenerative preheating in'stoves, without control by the blower con trol of the amount of air and fuel burned inthe direct heating after the stoves. 1

Fig. 3 is a diagrammatical view of apparatus for carry- -ing out the best modeof practicing the method by means of regenerative preheating in stoves, with'control by the blower control of the amount of air and fuel burned in .the direct heating after the stoves.

Referring to the drawings: 7

In Fig. 1, 41 is a blastfurnace supplied with air from blo wing engine 42, through the cold blast main 43, and

the hot blast main 44 and 45, bustle pipe 46, and tuyeres "47. Between the blast furnace 41 and the blowing engine '42, is a recuperator blast heater 48, having a blast inlet 49, a blast outlet 50, a gas burner 51 and a stack 52.. In

this recuperator, blast furnace gas from source 53- is burned in a manner similar to that used'in firing the customary blast furnace stove.

The blast, which has now been initially heated to a temperature within the capabilities of recuperators, is delivered to a final heating and humidifying chamber 54, having a blast inlet 55, a blast outlet 56 and a burner 57. Burner 57 is supplied with a gas containing a high percentage of hydrogen from source 58 through valve 59 and pressure booster 6t Burner 57 is arranged with a suitably cooled nozzle 61 located in the center of the blast stream.

Additional oxygen can be introduced into the blast as required, from a source of oxygen 62 through a valve '63 and pressure booster '64, or it can be introduced at atmospheric pressure into the inlet of the blowing engine 42.

In order to secure a constant blast temperature and humidity, the cold blast air from the blowing engine 42 is humidified to a'selected level by adding steam from a source 65 through a control valve 66.

'As an example of the performance of the process, let it be assumedthat 75,000 standard'cubic' feet of atmospheric air are to be heated to1400 F. and 11 grains of water are to be contained in the blastper cubic foot of dry air. The air is assumed to leave the blowing engine apricot 42-at 200 F. and to contain 5 grains of waerafterthe controlled steam addition. 6 The recuperator preheats the blast to 1100 R, a temperature within the scope of recuperator heaters. The heating and humidifying apparatus is assumed as being fired with a coke-oven gas of the following analysis:

Gross calorific value569 B.t.u. per cubic foot. When burned with air, each cubic foot of gas yields-- C0 Cubic foot 0.53 E 0 do 1.32 N do 436 The amount of air required to burn 1 cubic foot of this coke oven'gas is 5.45 cubic feet.

The heat'available from 1 cubic foot of this coke-oven 'gas is approximately 435 B.t.u., considering the flue gas exit temperature and the preheating of the air.

The heat required to raise 75,000 cubic feet of air with 5 grains moisture from 1100 F. to 1400 F. is approximately 428,000 B.t.u. Hence, 428,000+435=985 standard cubic feet of this coke oven gas are required to be burned per minute in the blast heating and humidifying apparatus 54. I

This amount of gas would yield 985x132 or about 13,000'standard cubic feet of H 0 which,'at 333 grains (avoir.) .per standard cubic foot, amounts try-approximately 433,000 grains of P1 0 per minute. This quantity, referred to 75,000 cubic feet of air per minute, is 6 grains of H 0 added to each cubic foot. I

The combustion of gas in the above example results 'in a deficiency of 1.5% oxygen in the blast air. This oxygen can be replaced from source'62, as previously designated.

If more humidity is desired in the blast furnace air, it is secured by reducing the amount of heating'efiected in the preheating recuperator '48, thus throwing more heating load on apparatus 54; thereby calling for the firing of more coke oven gas from line 57 which introduces more water (H O) as a product of combustion.

Referring to Fig. 2, the process is applied to blast furnace plants with existing hot blast stoves, and permits final blast temperatures higher than that available from heated refractories.

In Fig. 2, the parts or elements are the same as in Fig. 1, with the exception that the initial heating 'isby hot blast stoves 67 rather than a recuperator between blast inlet 49 and blast outlet 50. A mixer line 68 and valve 69 bypass sufiicient cold blast air to produce a uniform temperature in main 44.

As an example of the performance of the process in Fig. 2, let it be assumed that 75,000 standard cubic feet of air are to be heated to 2000 F. and that 25 grains of water are to be contained per cubic foot of dry air. The air is assumed to leave the hot blast stovesat 1500." F., and to contain 14 grains of water per cubic foot after addition of steam.

The heat required to raise 75,000 cubic feet of air with 14 grains moisture from 1500 F. to 2000 F. is approximately 806,000 B.t.u. Hence 806,000-2-415 (the heat available from 1 cubic foot of coke .oven gasin this example) :1940 standard cubic feet of coke oven gas required .to be burned perminute in the blast stream. This amount of gas would yield 1940x132 or about 2560 standard cubic feet of H 0, which at 333 grains (-avoir.) per standard cubic foot amounts to approximately 854,000grains ofH O per minute. This quantity, referred to 75,000 cubic feet air per-minute, is 1lf'g'rains of H 0 added to each cubic foot.

The combustion of gas in this example results in a deficiency of 3% oxygen in the blast air. This oxygen can be replaced from source 62, as previously designated.

It is not the purpose of the above description to specify particular apparatus, but rather, to clarify the presentation of process. The process is based on the heating and humidifying of blast air by burning directly in the blast air a gas containing a high percentage of hydrogen, and the control of the blast heating and of the blast humidification. The process of Fig. 1 accomplishes the addition of heat to blast furnace air beyond the practical scope of heating by recuperators. The process of Fig. 2 accomplishes the addition of heat to blast furnace air beyond the practical scope of heating by regenerative hot blast stoves.

Referring to Fig. 3, there is shown a typical existing blast furnace system comprising the blast furnace proper 10, stoves 11, and a blower 12, for supply of the total air in a line 9 for the furnace. The blower 12 is located in a central control station 8 and the air after preheating is fed to the furnace through a hot blast main 13. The hot blast main delivers the blast to a bustle pipe 14 which feeds the air to the tuyeres 15 in the blast furnace. The cold blast air main 9 delivers the total air for the blast furnace past a snort valve 16 to a bypass mixer line 17 and line 18 beyond the same leading to the stoves. As shown, the stoves are heated up by combustion chamber 19 in alternation with the preheating of air, which air leaves the stoves through the combustion chamber 19 at the entering part of the hot blast main 13. The bypass mixer line 17 discharges into the combustion chambers 19 of the stoves 11 in series, when they are operable for preheating of the blast to temper the heat of the air to a constant temperature as it flows through the hot blast line 13 to the bustle pipe 14.

. The lines 17 and 18 are provided with valves 20 to control the proportions of the total volume of air that flows to the stoves 11 and around the stoves to mix with the air from the stoves, to maintain the hot blast temperature constant. These valves 20 are controlled by thermo-responsive means in the form of a thermocouple 21 in the hot blast line 13 with connections to the valves 20 to open the valve 20 in the line 18 to the stoves and correspondingly close the valve 29 in the bypass mixing line 17 as the temperature of the air in the hot blast line drops.

This mechanism is adjusted by controls in the furnace area control station. The air from the mixer line 17 enters the combustion chambers 19 through branches 17'.

In accordance with the present invention, a direct heating burner 22 is located in the hot blast line or main 13 directly before the bustle pipe 14, which comprises a special burner assembly 22 with coke oven gas burner nozzles (not shown). Combustion air for sup porting this combustion is supplied to the burner 22 from the cold blast main 9 before the line 18 to the stoves 11, and preferably, from a region in the cold blast line 9 between the bypass line 17 and the snort valve 16, by a temperature augmenting air line 24 which terminates in an air manifold (not shown) for the coke oven gas burner 22. The temperature augmenting air line 24 is provided with a butterfly valve 25 and an orifice plate 26 with conventional means 27 for operating the valve 25 by, and in accordance with, changes in pressure across the orifice plate 26.

The means 27 is a volume proportioning control which operates the butterfly valve 25 to maintain a constant proportion of combustion air to the coke oven gas burners 23 in relation to the total blast air in line 9. The volume of the total col-d blast air in line 9 is measured by the existing orifice plate and volume measuring equipment 9' at the blower house 8, in which the impulse there from the existing orifice plate is transmitted to the volume proportioning control 27. Fine manual adjustment of the volume proportioning control 27 is based upon the temperature readings of four thermocouples 28 in the tuyere stocks of the blast furnace. Coke oven gas is admitted to the burner 22 by a flow control valve 31 in proportion to the combustion air, in response to a fuel-to-air ratio controller 30 receiving its impulse by line 37 from the orifice plate 26 in the combustion air supply line 24. The output signal of the fuel to air ratio controller 30 actuates the reverse acting bypass valve 31 on a special positive displacement coke oven gas compressor 32 which is of the constant speed, constant volume and constant discharge pressure type. A safety shutoff valve 33 is placed in the section 34 to the coke oven gas compressor which is actuated by a pressure switch 35 in the hot blast main 13, to close upon failure of pressure in the cold blast main 9. An override control 36 on the volume of proportioning butterfly valve 25 in the combustion air supply line 24 closes the butterfly valve 25 in the line 24 at a preset minimum flow through this line to suit the minimum turndown rate of the coke oven gas burner 22.

With the procedure as above-described in connection with Fig. 3, the method of increasing the humidity of the blast, while concurrently augmenting the heating of the hot blast from the stoves is, in general, the same as is above-described in connection with Fig. 2.

With this improvement as described in Fig. 3, the further heating of the hot blast air for the furnace utilizes part of the total air intended for support of the combustion of the coke bed in the hearth of the furnace, directly in the hot blast from the stoves and before the furnace tuyeres, so that the total air for the blast furnace remains the same while the products of combustion of the gas in the hot blast, CO and H 0, react with carbon in the furnace, producing useful reductants in the blast furnace process.

To this end, the thermocouple in the hot blast main or line operates a control in the furnace area control station to operate the butterfly valves in the bypass line and in the portion of the cold blast main or line after the olftake region of the bypass mixer line so that less air flows through the mixer line and more air through the stoves as their temperatures drop, thus keeping the temperature of the preheated air constant in the hot blast line or main. The blast furnace operating personnel can release the pressure in the blast furnace by operating the snort valve which exhausts air from the blower to the atmosphere from the cold blast line or main in advance of the bypass mixer line and the stoves.

To raise the temperature level of the hot blast from the stoves without alteration of the presently installed equipment for blast furnace systems, the temperature augmenting air line is connected to the cold blast main or line after the snort valve to feed part of the "total air to an air manifold, and the fuel gas line with a compressor is connected to feed fuel gas to a manifold, around the hot blast main. This air is a part of the total air from the blower and so, the total air for the blast furnace remains the same. These manifolds feed burners which discharge into the hot blast main or line.

The temperature augmenting air line is provided with a butterfly valve and an orifice plate operatively connected together under control of an element in the furnace area control station to adjust the air for these burners. Feed of air and gas to these burners is constant, whereas the butterfly valves for the bypass mixer line and for the cold blast main or line to the stoves are adjusted from a control station under the impulse of the thermocouple in the hot blast line from the stoves which is located therein before the burners for the temperature augmenting air line.

The invention is hereinabove-set forth as embodied in a particular form of construction but may be variously embodied within the scope of the claims hereinafter made.

a I claim:

1. In a process of heating and humidifying the blast for 7 n ftnetalliir gical"blastfurnace, which comprises: blowing "coldc blast air-for: the blastrof the'furnace through ap'reheating medium therefor and thereby preheating the blast for the furnace, thereafter augmenting the heat of the blastvfrbmsaid medium by burning combustible fuel with ,partof the total air of the blast directly in the preheated blast, and thereafter delivering the heat augmented hot blast'intothe hearth in the blast furnace While Charged with water vapor to a predetermined constancy of humidity, thetimprovement comprising the steps of; eifecting said augmenting of the'hea't of the blast by burning a hydrogen containing fuel as the combustible fuel directly in the blast and thereby charging the'blast with a substantial-part of the water vapor'for said predetermined constancy of humidity as a product of said combustion, and addingthe rer'nainder 'of the'total amount of vapor to form said predetermined constancy of humidity in the form of steam to the cold blast air after the blowing step, but before'it passes into the aforesaid preheating medium for the blast.

2.t-A process "as claimed in claim 1, and in which the preheating bythe aforesaid preheating medium is effected by 'recuperative heating of the blast by indirect heat exchange thereof with hotproducts ofcombustion. I 3. A process as claimed in claim 1, and in which the preheating by the aforesaid preheating medium is effected by regenerative heating of the blast by heat'previously stored in heat storing material. 7

4. A method as claimed in claim Land in which'the amounts of the-hydrogen containing gas th'at'is burned as aforesaid, and of t'hejpart of the total air of the blast .thatisburne'd withthe gas, is controlled by, and in acfcbiid'ance with, variations 'in the total amount of'cold 'bla'stair' blown in'the'fiIst aforesaid blowing step for the blast.

-5.' In aproces's of heating and humidifying the blast for a metallurgical'blast furnace, which comprises: blowing coldblast air for the blast of thefurnace through .a preheating mediumJtherefor and thereby preheating the blast forzthefurnace, thereafter augmenting the heat of the Y 8 blast from said me'diumby burning combustible ffllel withflpart of the-total air of theblast directly-in thefpieheated blast,-and thereafter delivering the heat augmented hot blast into the hearth in the blast furnace while charged withfwatervapor to a predetermined constancy ofhhfni'd ity, theimprovement'comprising the steps'of; effecting said augmentingof the heat of the blast by burning ah'ydrogen containing fuel as the combustible fuel directly in'the blast and thereby augmenting the heat thereof "by at least 300 F. and at the same time, charging'the blast with at least about one-half of the total amount of water vapor required 'for said predetermined constancy of humidity as a product of said combustion, and addingthe remainder of the total amount of vapor required 'to form said predetermined constancy of humidity in the'form'of steam to the cold blast air after'theblowing stepfbut before it passes into the aforesaid preheating medium for the blast. g

6. A process as claimedin'claim 5, andin which the preheating by the aforesaid preheating medium is effected by recuperative heating of the blast to 'not more than 1100" F. with indirect heat exchange thereof with hot products-of combustion, and the burning of thegasdirectly in the hot blast is effected to augrnent'the heat thereby at least 300 F.

7. A process asclaimed inclaim 5, and inwhich the preheating by the aforesaid preheating medium is effected by regenerative heating of the blast to not more than 1500 'F. with heat previously stored in heatstoringmaterial, and the burning of the gas directly in the hot blast iseffected to augment the heat thereof by at least 500,F.

8. A method as claimed in claim 5, and 'in which" the amounts of the hydrogen co'ntainiriggasthat isburned-as aforesaid, and of the part of the total'air'of the *blast that is burned with the gas is controlled by, and-in accordance with, variations in the total amount of cold blast air blown in the first aforesaid *blowing-step foi' the blast.

'No references cited. 

1. IN A PROCESS OF HEATING AND HUMIDIFYING THE BLAST FOR A METALLURIGICAL BLAST FURNACE, WHICH COMPRISES: BLOWING COLD BLAST AIR FOR THE BLAST OF THE FURNACE THROUGH A PREHEATING MEDIUM THEREFOR AND THEREBY PREHEATING THE BLAST FOR THE FURNACE, THEREAFTER AUGMENTING THE HEAT OF THE BLAST FROM SAID MEDIUM BY BURNING COMBUSTIBLE FUEL WITH PART OF THE TOTAL AIR OF THE BLAST DIRECTLY IN PREHEATED BLAST, AND THEREAFTER DELIVERING THE HEAT AUGMENTED HOT BLAST INTO THE HEARTH IN THE BLAST FURNACE WHILE CHARGED WITH WATER VAPOR TO A PREDETERMINED CONSTANCY OF HUMIDITY, THE IMPROVEMENT COMPRISING THE STEPS OF, EFFECTING SAID AUGMENTING OF THE HEAT OF THE BLAST BY BURNING A 